Television scanning and synchronizing system



2 Sheets-Sheet 1 P. T. FARNSWORTH Filed may 5, 1950 TELEVISION SCANNING AND SYNCHRONIZING SYSTEM June 24, 1941.

INVENTOR ATTOIRNEY Mhhhlllhhl K EHIIIIIIIIIII June 24, 1941. P. T. FARNSWORTH 2,246,625

TELEVISION scmmme AND smcrmouxzme SYSTEM Filed May 5, 1930 2 Sheets-Sheet 2 INVENTOR. PH/LO T. FARNSWORTH.

ATTORNEY Patented June 24, 1941 TELEVISION SCANNING AND SYNCHBONIZ- ING SYSTEM Phllo 'r. Farnrworth, San Francisco, Calif assignor, by meme assignments, to Farnsworth Television a Radio Corporation, Dover, DeL, a

corporation of Delaware Application May 5, 1930, Serial No. 9,984

42 Claims.

My invention relates to means for scanning the pictured field in a system for the electrical transmission of pictures, and particularly to such scanning means as employed in cathode ray transmitting and receiving devices.

Among the objects of my invention are: First. to provide electrical means for scanning the pictured field in a discontinuous path, each of the scanning lines traversing the picture in the same direction; second, to provide a system whereby the transmitting and receiving scanning means are accurately held in synchronism; third, to provide a scanning system wherein the picture intensities are substantially uniform over the entire field; fourth, to provide a. system wherein slight phase differences between transmitting and receiving scanning systems are accompanied by no loss in the definition of the transmitted picture, but merely inslight displacements thereof; fifth, to provide a means of extinguishing a scanning beam completely during its return or non-scanning sweep; and sixth, to provide a scanning system wherein no filters or other devices causing phase distortion need be employed in order to separate the synchronizing impulses from the picture current.

My invention possesses numerous other objects andfeatures of advantage, some of which, with the foregoing, will be set forth'in the following description of my invention; It is to be understood that I do not limit myself to this disclosure of species of my invention, as I may adopt variant embodiments thereof within the scope of the claims.

Referring to the drawings:

Figure 1 is a diagrammatic representation of a television transmitter as employed in my system.

transmitter of the type described in my copending applications Serial Numbers 159,540, 245,334, 270,673, and 321,805. This wave serves to move the discharge path so as to scan the transmitted image gradually from one side to the other, and then to return it almost instantaneously to its initial position, after which the operation is repeated. The rapid change of current on the return half of the wave produces a powerful voltage pulse across the scanning coils,

and this pulse is applied to prevent the flow of picture current during the return sweep, effectively cutting oif the scanning beam during this period.

The eifect on the picture current is equivalent to the scanning beam traversing an area of zero illumination on the return slope of the scanlnng wave. When the picture currents are transmitted the current pulses of the scanning frequencies, which are more powerful than any of the picture pulses are therefore transmitted simultaneously therewith. At the receiving end of the system these powerful pulses are used for the dual purpose of cutting off the receiving scanning beam during the return stroke, and of holding in synchronism a generator of scanning currents of the same type as is used in the transmitter.

Similar generators of scanning frequencies are used for both the low or picture frequency scanning and the high or scanning frequency scanning. At the receiver each of these generators is adjusted to oscillate naturally at approximately the proper scanning frequency, and the re- Figure 2 is a similar representation of a rescanned by the system here disclosed.

Co..sidered in general terms, my system compulses a generator of scanning current having a wave form comprising substantially straight lines 01' different slopes, l. e., a saw-tooth wave. This current wave is passed thru an inductive circuit such as the deflecting coils of a television celved picture impulses, properly applied to the generators, serve to hold them in step even tho their natural frequency may deviate from the fre uencies of the transmitter by as much as 10 o- Describing my invention with direct relation to the system described in applications for Letters Patent above referred to, the transmitter tube used comprises an evacuated envelope Ill having a photo-electric cathode II and anode screen 12 and a target l3 enclosed therein. The target is surrounded by a shield it having an aperture II. The image to be transmitted is focused upon the photo-sensitive surface, liberating electrons which are drawn in the direction of the anodes by means of a potential applied from the source I 6. These electrons are focused by methods described elsewhere and not here shown to form an electrical image in the plane of the aperture IS, the electronsfrom a single element of the image entering the aperture and flowing currents varying at a low or picture frequency which may be from 12 to or more cycles per second, and the other varying at the high or scanning frequency whose value is dependent upon the number of scanning lines or the size of the picture element which it is desired to transmit. Since the coils and the generators which supply the scanning currents difler only in electrical dimensions, only one set is shown, it being understood that a second similar set is used in practice.

The generator used to supply the scanning current is preferably that described in the copending application of Farnsw-orth and Lubcke,

Serial No. 449,985, filed May 5, 1930. It comprises a condenser which is charged by a suitable potential source 26 thru a. resistor 21. Bridging the condenser is a gas discharge tube 28, which has a breakdown potential within the voltage range provided by the source 26. When the condenser 25 is charged to the breakdown value of the tube 28, a discharge takes place which permits the condenser voltage to drop almost instantly. This causes the discharge to break, and the condenser is then gradually recharged thru the resistor 21. The adjustments are such that neither complete charge nor complete discharge of the condenser takes place, and as a result the voltage on the condenser varies substantially asshown in the curve 30 of Figure 3A, referred to the axis X-X.

This voltage wave is applied thru the coupling condenser 3| to the grid or control electrode of the vacuum tube 32, the grid being biased thru a resistor 33 by a source 34 so that the grid voltage varies as is shown by the curve 36 when referred to the axis X'-X.

The tube 32 is preferably of the screen grid I type, having extremely high internal impedance.

Its output circuit comprises a distorting network which, in its simplest form, is an inductor 36 in series with a resistor 31. This network has a low impedance as compared with that of the tube, and hence the plate current of the tube is substantially as shown by curve 38, Figure 3B.

The voltage produced across the network is the sum of a resistance term which is directly proportional to the current in the network, and is illustrated by the curve 46, Figure 3C, and an inductive drop which is proportional to the rateof-change of the current and is of the form shown in curve 4|, Figure 3C. The sum of these two terms is a voltage wave of the form shown in Figure 3D and comprises a powerful negative voltage pulse, followed by a gradual increase in voltage.

The voltage wave generated across the distorting network is applied to the grid of a low Considering the tube 42 at zero bias, and maximum current flow therethru, the powerful negative pulse of the control wave serves to cut the plate current to zero practically instantly. This change in plate current causes an extremely high voltage rise in the inductive output circuit, the eflect being the same whether the transformer 44 be used or whether the tube be connected directly to the scanning coil 21, The intensity of the input voltage pulse is such that the current is reduced to zero in spite of this great rise in plate voltage. This sudden change in plate 'current is what causes the steep return slope of the scanning wave. The sloped portion of the control wave then permits a gradually increasing current to flow in the plate circuit, causing the scanning slope of the current wave. The wave form is substantially that shown in curve 50, Figure 3E. The voltage induced across the scanning coils has a wave form substantially as shown in curve SI of the same figure. A resistor 52 is preferably connected across the output circuit in order to suppress shock-excited oscillations of high frequency in the output system.

A small pickup coil 53 is connected in series with the output resistor ll of th transmitting tube, and is positioned in the stray field from the scanning coils 2!. The pickup coil is phased so that the intense pulse generated by the return slope of the scanning wave will produce a voltage which is in opposition to the electron current flow thru the resistor. This causes an extremely small current to flow thru the resistor and the capacity between the target l3 and the shield I4, to produce a voltage drop of suflicient magnitude eifectively to nullify the picture current.

The actual magnitude of this voltage pulse as it appears across the resistor I1 is, of course, extremely small, but it is amplified together with the picture voltage and is preferably made of sufiicient value to produce 100% modulation of the radiated carrier current, As has been explained above, the scanning coils of the low-frequency scanning generator are also positioned adjacent those of the high-frequency scanning generator. Inherently, therefore, similar pulses at the low frequency are induced into the coil 53 and result, in exactly the same manner, in pulses in the composite signal which differ from the high-frequency synchronizing pulses only in their frequency and necessarily larger duration. In order to obtain good quality of reproduction the modulation of the carrier by the picture currents is ordinarily of the order of 30%. The result is that a series of powerful pulses, coinciding in frequency and phase with the return slope of the scanning wave is transmitted together with the picture frequencies.

The transmitted carrier is picked up on a receiver of the type shown diagrammatically in 'Figure 2, the waves being collected by the animpedance tube 42 thru a coupling condenser 43. I

tenna 66, amplified, and detected by th amplifier-detector 6|, which has an output tube 62. This tube is coupled by the plate and grid resistors 63 and 65 and the coupling condenser 66 to the grid or control electrode 61 of a cathode ray receiving tube or "oscillight 68.

The oscillight has an anode 69 to which a posi-- tive potential is applied from the source 16 to accelerate a cathode beam from a filament or emitter II, this beam being modulated by the control electrode. The beam is received upon a fluorescent or phosphorescent screen 12, and is deflected by coils 13 to scan the pictured area. As is the case with the transmitter, coils are proassume resistor is preferably of about 4 times the value of the resistor 21', and may be of the order of a megohm. The plate resistor 63 and grid resistor 05 are preferably of much smaller value, being of the order of 2,000 ohms and 50,000 ohms respectively.

As has already been pointed out. the received wave comprises strong negative pulses coinciding in phase with the return slope of the scanning \vave produced by the oscillator. These pulses serve completely to cut off the scanning beam during the return sweep. At the same time these negative impulses are impressed thru the resistor 11 upon the oscillation generator, and serve to hold it in phase. Experience has shown that this phasing action is perfectly accomplished even tho the natural frequency of the generator may be plus or minus 10% of! of the received frequency.

The voltage applied to the grid i! by the synchronizing pulses may be of the order of 30 volts, completely to extinguish the scanning beam. A relatively small portion of this voltage, perhaps 4 or 5 volts, is applied thru the resistor 11 to the condenser 25', but this is sufilcient to determine the period of breakdown of the gas discharge path, and to hold the generator accurately in step. n the other hand, the resistor II has an extremely high value as compared to the resistors 63 and 65 in parallel, and therefore the voltage delivered back thru the resistor from the generator to the grid of the receiving tube is negligibly small, and does not affect either the definition or the light distribution of the picture.

Since the synchronizing pulses are represented by a much higher degree of modulation of the carrier than are the picture currents and are therefore applied to the oscillation generator at much greater amplitude, there is no tendency for the generator to synchronize with the darker portions of the picture, as would otherwise be the case. Thus if the relative percentages of modulation are 100 and 30, as suggested above, and the value of the resistor i1 is such as to apply volts to the condenser 15, the voltage applied thereto by the picture frequencies will not exceed 1 /2 volts, and a much smaller disparity than this will assure perfectly stable synchronization.

In practice, both the low frequency. and the high frequency generators ar connected to the grid 61 in similar fashion, and receive the same impulses. The natural frequencies of the two generators are so far separated that there is no tendency for the synchronizing impulses to become confused. The generators are preferably adjusted so that the proportion of the cycle occupied by the return stroke is the same for both low and high frequency generators. Under these circumstances, the low frequency generator is ferred from the high frequency to the low frequency generators, but the effect of this is simply to stabilize the low frequency generator on a subharmonic of the high frequency, and to maintain the high frequency at an integral multiple of the low scanning frequency. Were the low and high frequency synchronizing pulses of equal duration, there would be a certain tendency to instability, since the high frequency generator might operate upon any of a plurality of higher harmonics of the low frequency. The longer period of the lowfrequency synchronizing pulse gives sufi'lcient stabilization to prevent this tendency toward instability.

In the appended claims, the term critical characteristic is utilized to define the nature of the synchronizing signals of the present invention and applies to any characteristic by virtue of which a signal having one such critical characteristic may be distinguished from a signal having a different one of such critical characteristics.

The advantage of my system of scanning may readily be seen by reference to the scanning patterns shown in Figures 4 and 5. Where a sine wave 80, as shown in Figure 4, scans a line 8i,-a slight phase error, such as is produced when the receiver scanning system lags slightly behind the transmitter, the received image of thelines will appear to divide into two, each of less intensity and displaced equally on opposite sides of the true position of the line as is shown by the dots of a received picture even tho the phase displacement may be so small that no definite and appreciable separation of the images occurs.

With my system such small phase variations merely produce a slight shift in the position of the image, and phase differences which would produce a marked blurring with sine wave scanning merely produce an unappreciable displacement when my system is used.

This may be appreciated by reference to Figure 5, where a line 83, scanned by the discontinuous wave 84, is merely displaced to the position of the line I! by a phase shift in the receiver. Any additional effect will be limited to a slight blurring or transposition at the edges of the field, of the same character as is produced when a moving picture is slightly out of frame.

Another advantage of my system is that the illumination of the picture field is much more uniform than can be produced by the sine wave. In sine wave scanning the outer edges of the picture are much more brilliant than is the central portion of the field; with this system of scanning such slight differences in brilliancy as do occur are in favor of the central portion of the field, and it is in the central field that the objects of prime interest in the picture ordinarily occur.

Even if the scanning beam is not totally extingulshed during the return slope of the scanning wave, the results are better than with sine wave scanning. This is because the illumination on the returned sweep of the beam is inversely proportional to its speed of travel, and there fore, if a secondary image is produced, it will only be about $5 as bright as the primary image, which makes it of negligible importance. The complete extinction of the returning beam is, however, to be preferred.

I claim:

1. A television system comprising means for developing a beam of electrons, means for exposing said beam to the influence of a scanning wave which normally would cause said beam repeatedly to be deflected relative to said target relatively slowly in one direction and relatively rapidly in another direction, and means for substantially extinguishing said beam during the rapid portion of the deflecting cycle.

2. A television system, comprising cathode ray apparatus adapted to develop a beam of electrons wherein the intensity of said beam of electrons varies in accordance with the illumination of the various elemental areas of the picture transmitted by said system, means for causing deflecting movement oi said beam of electrons, and means operably associated with said firstnamed means for substantially extinguishing said beam of electrons during a predetermined portion of the deflecting cycle.

3. In combination, a scanning device comprising means for generating a beam of energy, means for controlling the intensity of said beam, deflecting means including a sawtooth wave generator for deflecting said beam in one direction at one rate of speed and in another direction at another rate of speed, and means associated with said intensity control means for cancelling said beam only during the time which would otherwise be occupied by its deflection in one of said directions.

4. In a television system, cathode ray apparatus adapted to develop a beam of electrons wherein the intensity of said beam of electrons varies in accordance with the illumination of the various elemental areas of the picture transmitted by said system, means for causing scanning movement of said beam of electrons, and means controlled by said first named means for suppressing the effect of said beam of electrons during a predetermined portion of the scanning cycle.

5. A television receiving system for receiving and reproducing a television signal including picture components representing illumination and synchronizing components comprising a cathode ray signal reproducing device including means for developing a beam of electrons, means for utilizing said signal to modulate said beam whereby said beam is substantially extinguished during periods corresponding in frequency to said synchronizing pulses, scanning means for periodically deflecting said beam in one, direction at a predetermined rate of speed and tending to deflect said beam in an opposite direction at a greater rate of speed, and means for utilizingsaid synchronizing components so to synchronize the operation of said scanning means that said deflections in said opposite direction correspond in time to the periods during which that beam is substantially extinguished.

6. A television receiving system for receiving and reproducing a television signal including picture components representing illumination and synchronizing components comprising a cathode ray signal reproducing device including means for developing a beam of electrons, means for periodically deflecting said beam in one direction at a predetermined rate of speed and tending to deflect said beam substantially in an opposite direction at a greater rate of speed, means for utilizing said synchronizing components to control the operation of said deflecting means, means for controlling the intensity of said beam to provide a predetermined intensity thereof corresponding to black in the reproduced image in the absence of said picture components, and means for so applying said signal to said intensity control means that said picture components increase the intensity of said beam proportionally to their amplitude and said synchronizing components tend to decrease the intensity of said beam beyond said predetermined value during the period of deflection in said opposite direction.

7. A television receiving system for receiving and reproducing a television signal including picture components and synchronizing components, comprising signal repeating means for said picture components and said synchronizing components, and picture reproducing means supplied from said repeating means and operable for reproducing a picture in response to said picture components, said picture-reproducing means being responsive to and held in synchronism only by said synchronizing components having a polarity in the direction of the minimum picture components and of greater amplitude in said direction than picture components which would be ipiroduced by scanning an area of zero illumina- 8. A television receiver adapted to receive a composite synchronizing signal including a first series of synchronizing components of a predetermined frequency and having a predetermined critical characteristic and a second series of synchronizing components interspersed with said first series, having a diflerent predetermined frequency and having a different critical characteristic, comprising a first scanning circuit for operation at said first-mentioned frequency, a second scanning circuit for operation at said second-mentioned frequency, means for applying substantially all frequency components of said composite synchronizing signal to said first and said second scanning circuits, means responsive only to said first series of components in said composite signal for synchronizing said first scanning circuit, and means responsive only to said second series of components in said composite signal for synchronizing said second scanning circuit.

9. A television receiving system for receiving and reproducing a television signal including picture components representing illumination and synchronizing components having a. polarity in the direction of the minimum picture components and of greater amplitude in said direction than picture components corresponding to black, comprising a cathode ray signal reproducing device including means for developing a beam of electrons, means for utilizing said signal to modulate said beam, means for deflecting said beam, and an aperiodic signal path for applying substantially all frequency components or said picture and said synchronizing components to said deflecting means, thereby to utilize said synchronizing components for controlling said deflecting means.

10. The method of scanning a target in a cathode ray tube which comprises developing a, beam of electrons, exposing said beam to the influence of a scanning wave which would normally cause said beam repeatedly to scan said target relatively slowly in one direction and relatively rapidly in another direction, and substantially extinguishing said beam during the rapid portion of the cycle.

11. For use in a television receiving system for receiving and reproducing a television signal in- 7 and reproducing a television signal, comprising a cathode ray signal reproducing device including means for generating a beam of electrons, control means for modulating said beam, means including a non-resonant oscillator circuit for causing said beam to scan a target, signal repeating means for repeating said television signal, means coupling said repeating means to said control means for the application of the signal thereto, and aperiodic means connecting said repeating means to said oscillator for applying substantially all frequency components of said television signal to said oscillator thereby to control the operation thereof.

13. A television receiving system for receiving and reproducing a television signal including picture components and synchronizing components,

comprising a cathode ray reproducing tube including means for generating a beam of electrons, control means for modulating said beam, and a target, a non-resonant oscillator for scanning said beam across said target, and an aperiodic connection between said control means and said oscillator for applying substantially all frequency electrons, a control electrode for controlling said beam, and a target adapted to be impacted by said beam, means for applying said television signal to said control electrode, a slope wave gen-u erator connected to deflect said beam of electrons to scan said target and including a. discharge device bridging a condenser, means for charging said condenser to a predetermined operating potential of said device, and circuit means operably connected between said controlelectrode and said condenser to apply said signal thereto.

15. A television receiving system for receiving and reproducing a television signal including picture components and synchronizing components, comprising a cathode-ray picture reproducing tube having a control electrode and a target, means for applying said signals to said control electrode, a slope-wave generator connected to deflect the beam of cathode rays to scan said target, and means for applying the potential of said control electrode to said generator to control its operation in accordance with said synchronizing components.

'16. A television receiving system for receiving and reproducing a television signal including picflect the beam of cathode rays to scan said target and including an ionic discharge device, and means for applying the potential of said control electrode to said discharge device to determine its instant of discharge, thereby to'control its operation in accordance with said synchronizing components.

17. A television receiving system for receiving and reproducing a television signal including picture components and synchronizing components, comprising a cathode-ray signal reproducing tube having a control electrode and a target, means for applying said television signal to said control electrode, a slope-wave generator connected to deflect the beam of cathode rays in said tube to scan said target and including an ionic discharge device bridging a condenser,

means for charging said condenser to the breakdown potential of said device, and a resistor connecting said control electrode to said condenser to apply a synchronizing voltage thereto.

18. A television system for receiving and reproducing a television signal including picture components and synchronizing components, comprising a cathode-ray signal reproducing tube having a control electrode for receiving said television signal and a target, means for applying said television signal to said control electrode, a slope-wave generator connected to deflect the beam of cathode rays to scan said target and including an ionic discharge device bridging a condenser and a resistorthrough which said condenser is charged to the breakdown potential of said device, and a resistor connecting said control electrode and said condenser and having a value materially greater than said charging resistor.

19. In a television receiving system comprising light reproducing apparatus and scanning apparatus, each controllable by received pulses, said light reproducing apparatus comprising means for generating a beam of electrons and said scanning apparatus comprising means for deflecting said beam of electrons in one direction at a relatively slow rate of speed during trace intervals and in another direction at a relatively fast rate of speed during retrace intervals, the method of operation which includes the steps of supplying mixed synchronizing and picture signal pulses to each of said apparatus for controlling it primarily by pulses of only one of said types, and preventing each set of pulses from affecting the reproduced picture through the apparatus which it was not primarily'intended to control, by applying the synchronizing pulses to said light-reproducing apparatus in such sense assubstantially to extinguish said electron beam during said retrace intervals, and by applying said picture signal pulses to said scanning apparatus at an intensity less than 20. In a television receiving system for receiving and reproducing a television signal including picture components and synchronizing components, and employing electrical oscillations to scan an elementary area of variable illumination developed by means of an electron beam back and forth across a target at a relatively rapid rate in one direction and a slower rate in substantially the opposite direction, the method of operation which includes the steps of utilizing said television signal to control said variable illumination in sense and degree such that said scanning motion of said beam to develop a picture signal varying in accordance with the illumination of the various elemental areas of the picture to be transmitted, and means activated in synchronism with said scanning means for substantially suppressing said picture signal by substantially extinguishing said beam of electrons during a predetermined period of the scanning cycle.

22. A television transmitting system comprising means for developing a picture signal, means for periodically suppressing said picture signal during predetermined intervals and inserting in said signal during said intervals synchronizing signals or different frequencies and diiIerent critical characteristics, said synchronizing signals having a polarity in the direction of minimum picture signals and a greater amplitude in said direction than picture signals corresponding to zero illumination.

23. A television transmitter comprising a cathode ray picture signal generating tube, a picture signal circuit connected to said tube, a scanning circuit associated with said tube, means for generating scanning pulses in said scanning circuit, and means for coupling said scanning and picture signal circuits for inducing pulses of scanning frequency in said picture signal circult.

24. A television transmitter comprising a cathode ray picture signal generating tube, a coil arranged adjacent said tube for producing a magnetic field to deflect the cathode rays therein, means for generating a current of scanning frequency in said coil having a sawtooth wave form, a picture signal circuit connected to said tube, and a coil in said picture signal circuit coupled to said magnetic field to induce pulses of scanning frequency in said picture signal circult.

25. The method of television transmission which includes the steps of scanning a picture field to produce successive picture signal pulses each proportional to the illumination of the elementary area of the field instantaneously under scansion, and interspersing said pulses with synchronizing pulses corresponding in sign with those picture signal pulses produced by scanning an area of less than average illumination and of an amplitude greater than those picture signal pulses which would be produced by scanning an area of zero illumination.

26. In the art of television wherein synchronizing pulses are required for synchronizing operations at the transmitting and receiving stations, the method of operation which comprises developing picture signals varying in intensity in accordance with conditions of light and shade of the representation to be transmitted, developing synchronizing pulses having a polarity in poses; the method of operation which comprises developing said effects substantially out of phase with respect to the picture signals developed for conditions of light on the transmitted picture and of substantially greater amplitude than picture signals which would be produced by scanning an area of zero illumination.

28. In the art of television wherein picture signals and synchronizing signals are developed and appear in the same circuit, the method of producing said signals with distinguishing characteristics which comprises developing picture signals in said circuit and developing the synchronizing signals in said circuit in the op site polarity of that of the picture signals in said circuit which are representative of conditions of light at the subject for transmission and with an amplitude greater than the picture signals for corzditions of entire absence of light at the sub- Jec Y 29. In the art of picture transmission wherein picture signals representing illumination are developed and wherein synchronizing signals of two different frequencies are required for synchronizing purposes, the method of operation which consists in developing a first series of synchronizing signals at a predetermined frequency and having a predetermined critical characteristic, developing a second series of synchronizing signals at a different predetermined frequency and having a diil'erent critical characteristic, both of said synchronizing signals having a polarity in the direction of the minimum picture signals and being of greater amplitude in said direction than picture signals which would be produced by scanning an area of zero illumination, and transmitting said two series of synchronizing signals.

30. In a television system, the method of signalling which comprises scanning a picture subject along a series of lines to develop for each line of scanning picture signalling impulses varying in amplitude between a minimum and a maximum value determinable by the intensity of light and shadow on the subject, producing synchronizing signalling impulses following in time relationship each series of picture signalling impulses for each line of scanning, reversing the polarity oi the synchronizing impulses to produce a signal in the direction of the minimum picture signal and of a greater amplitude in the direction of minimum picture signal than any produced picture signal, and adding together the two produced series of signals to produce a composite series of signals representing both the picture subject and the synchronizing impulses.

31. In a television system, the method of signailing which comprises scanning a picture subject along a series of lines to develop for each line of scanning picture signalling impulses varying in amplitude between a minimum and a maximum value determinable by the intensity of light and shadow on the subject, separately producing synchronizing signalling impulses following in time relationship each series of picture signalling impulses for each line of scanning,

reversing the polarity of the'synchronizing than any produced picture signal, and adding together the two produced series of signals to produce a composite series of signals representing both the picture subject and the synchronizing impulses.

32. In a television system, the method of signalling which comprises scanning a picture subject along a series of lines to develop for each line of scanning picture signalling impulses varying in amplitude between a minimum and a maximum value determinable 'by the intensity,

transmitter, injecting pulses in said picture sigcorresponding in frequency to the frequency of the steeper slope portions of said scanning current wave, and utilizing said pulses to interr'upt the direct current at said receiver.

36. In a television system wherein the directcurrent component of the picture signal is suppressed in transmission and re-establlshed at a recelver,'the method of operation which includes the steps of using a scanning current having a wave form comprising substantially straight lines resenting both the picture subject and the syning in amplitude between a minimum and a maximum value determinable by the intensity of light and shadow on the subject, producing synchronizing signalling impulses of diiferent duration for line and frame synchronizing following in time relationship each series of picture signalling impulses for each line of scanning, re-' versing the polarity of the synchronizing impulses to produce a signal in the direction of the minimum picture signal and of a greater amplitude in the direction of minimum picture signal than any produced picture signal, and adding together the two produced series of signals to produce a composite series of signals representing both the picture subject and the synchronizing impulses.

34. In a television system, the method of signalling which comprises scanning a picture sub- Ject along a series of lines to develop for each line of scanning picture signalling impulses varying in amplitude between a minimum and a maximum value determinable by the intensity of light and shadow on the subject, producing synchronizing signalling impulses of different duration for line and frame synchronizing following in time relationship each series of picture signalling impulses for each line of scanning, electrically reversing the polarity of the synchronizing impulses to produce a signal in the direction of the minimum picture signal and of a greater amplitude in the direction of minimum picture signal than any produced picture signal, and adding together the two produced series of signals to produce a composite series of signals representing both the picture subject and the synchronizing impulses.

35. In a television system wherein the directcurrent component of the picture signal is suppressed in transmission and re-established at a receiver, the method of operation which includes the steps of using a scanning current having a wave form comprising substantially straight lines of unequal slope to scan a picture area at a of unequal slope to scan a picture area at a transmitter, injecting pulses in said picture signal corresponding in frequency to the frequency of the steeper slope portions of said scanning current wave, and utilizing said pulses to interrupt the direct current at said receiver, and to synchronize the scanning system thereof.

37. Th method of electrical transmission and reception of pictures which includes the steps of generating a train of picture signal pulses of varying intensity representing variations in light and shade of a picture to be reproduced, interspersing said picture signal pulses with synchronizing pulses of materially greater amplitude than the maximum amplitude of said picture signal pulses, and utilizing the mixed pulses at a receiver to control synchronization of motion of and to control the intensity of an electron beam scanning a picture field relatively slowly in one direction during trace periods and relatively rapidly in another direction during retrace periods, said mixed pulses being so utilized in phase and magnitude that said synchronizing pulses substantially extinguish said electron beam during said retrace periods, and said picture signal pulses being of insufficient amplitude to affect the synchronization of said motion.

38. A television method which comprises the steps of utilizing at a transmitter a scanning current having a wave form comprising substantially straight lines of unequal slope to scan the image to be transmitted for developing a picture signal, utilizing a voltage pulse induced by the steeper slope portion of said current wave to produce a pulse in said picture signal, and utilizing at a receiver said pulse to synchronize the generation of a similar scanning current.

39. A television method which comprises the steps of utilizing at a transmitter a scanning current having a wave form comprising substantially straight lines of unequal slope to scan the image to be transmitted for developing a picture signal, utilizing a voltage pulse induced by the steeper slope portion of said current wave to interrupt said pictur signal, and utilizing at a receiver said interruption of said picture signal to synchronize the generation of a similar scanning current.

40. A television method which comprises the steps of utilizing at a transmitter a scanning current having a wave form comprising substantially straight lines of unequal slope to scan the image to be transmitted for developing a picture signal, utilizing a voltage pulse induced by the steeper slope portion of said current wave to inreceiver, the method of operation which includes the steps of utilizing a scanning current having a wave form comprising substantially straight lines of unequal slope to scan a picture area at a transmitter, inducing a pulse in said picture signal corresponding to the steeper slope portion of said scanning current wave, and utilizing said pulse to interrupt the direct current component at said receiver and to synchronize the scanning 10 system thereof.

PHILO 'I'. FARNSWOR'I'H. 

